Facebook has added a new reaction feature to each post during last year which is still being implemented by today. Today, the Facebook reactions (Like, Love, Anger, Sad, Cry) can be added into your conversation between friends in messenger!
Apart from the common Facebook reactions, there will be a thumbs up and thumbs down button for opinion that you agree or disagree with. Reactions in Messenger is now in beta and has been available to certain users and soon will be available worldwide.
Source : Phonearena